Our aim is to undertake an intensive structure/function analysis of the catalytic and regulatory subsites of different acyl-CoA carboxylases from the same source in order to answer questions on (a) the organization of subsites in these complexes; (b) the degree of sharing of common structural features; and (c) the mechanism of assembly of multienzyme complexes and the advantages of the fusion of catalytic sites into multifunctional polypeptide chains. As a model for these general problems the acyl-CoA carboxylases of Pseudomonas citronellolis are under study to develop the techniques and affinity labeling reagents necessary to probe the molecular architecture of the highly integrated, multifunctional polypeptide chains present in the less tractable animal acyl-CoA carboxylases,